Method and apparatus for producing an image of the internal structure of an object

ABSTRACT

Inventions related to the intra-vision means, designed for production of visually sensed images of the internal structure of an object, in particular, of a biological object, are aimed at higher accuracy of determining the relative density indices of the object&#39;s substance in the obtained image together with avoiding complex and expensive engineering; when used for diagnostic purposes in medicine, the dosage of tissues surrounding those that are examined is decreased. X-rays from source  1  is concentrated (for example, using X-ray lens  2 ) in the zone that includes the current point  4 , to which the measurement results are attributed and which is located within the target area  7  of the object  5 . Excited in this zone secondary scattered radiation (Compton, fluorescent) is transported (for example, using X-ray lens  3 ) to one or more detectors  6 . By moving the said zone, the target area  7  of object  5  is scanned, and based upon population of the intensity values of the secondary radiation, which are obtained with the help of one or more detectors  6  and which are determined concurrently with coordinates of the current point  6 , judgment on the density of the object&#39;s substance in this point is made. Density values together with respective coordinate values obtained using sensors  11  are used in the means  12  for data processing and imaging to build up a picture of substance density distribution in the target area of the object.

This is a continuation of prior application Ser. No. 09/937,286, filedSep. 25, 2001, as the national stage of International ApplicationPCT/RU00/00207, filed May 30, 2000, now U.S. Pat. No. 6,754,304 B1.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The suggested inventions relate to the intra-vision means and aredesigned for producing visually sensed images of the internal structureof an object, in particular, of a biological object, with X-rays. Thepreferential applications include defectoscopy and medical diagnostics.

2. Description of the Prior Art

Various methods and devices of the said intended use are known, wheretraditional principles of projection roentgenoscopy are embodied. Insuch methods and devices, the visible image of the object's internalstructure, for example, tissues of a biological object, is obtained as ashadow projection. Density of the acquired image in each of its pointsis determined by the total attenuation of X-rays that passed through theobject on their way from the source to the detection means. The latteris either a fluorescent screen or an X-ray film, which should bechemically treated to get the image visualized (see PolytechnicalDictionary. Moscow, “Soviet Encyclopedia”, 1976 [1], p. 425; Physics ofimage visualization in medicine. Edited by S. Webb. Moscow, “Mir”, 1991[2], p. 40–41).

In the above mentioned known methods and devices, the image of a realthree-dimensional structure is acquired as the said two-dimensionalshadow projection, which interpretation requires from the specialist whocarries out object analysis, in particular, technical or medicaldiagnostics, respective experience and qualification and, in a number ofcases, is problematic. The reasons for this are low contrast, poorsignal to noise ratio, inevitable overlapping of the images ofstructural elements, impossibility of quantitative comparison betweenindividual local fragments by density. Sharpness and contrast of theacquired image also decrease under the influence of quanta of thesecondary Compton scattered radiation, hitting the detection means.

X-ray computer tomography methods and devices permitting to acquire atwo-dimensional image of a thin layer of a three-dimensional object areknown (V. V. Piklov, N. G. Preobrazhenskiy. Computational tomography andphysical experiment. The progress of physical sciences, v. 141, 3^(rd)ed., November 1983, p. 469–498 [3]; see also [2], p. 138–146). Suchmethods are using multiple irradiation of the object under study fromdifferent positions and registration of the radiation that passedthrough this object by a line of detectors. The obtained tissue densitydistribution of the object in the cross-section under study (targetcross-section) is discrete and achieved through computer-assistedsolution of combined equations, the order of which as well as the numberof resolution elements correspond to the product of the number ofpositions, from which irradiation is done, by the number of detectors.Doing irradiation in different cross-sections, one can obtain athree-dimensional image of the object based on a set of two-dimensionalby-layer images. Computer tomography means permit in principle to obtainan image of sufficiently high quality, and this image presents thepicture of tissues density distribution (in contrast to a picturespecific to integral absorption of a substance (for example, biologicaltissues), located in the path of radiation from the source to this orthat element of the observed projection.) But this is achieved through agreater number of positions, from which irradiation is done. In thiscase, the dose of radiation absorbed by the substance is higher, whichis undesirable (and in medical applications, is most frequentlyinadmissible). Presence of Compton scattered radiation is a nuisancefactor in this group of known methods and devices too. Both groups ofmethods and devices used for medical applications are also characterizedby the fact, that tissues and organs, which present no interest in thestudy but are located in the radiation path (both in front and behindthe target area), also suffer from intensive radiation (to a lesserdegree in the second group of methods and devices than in the firstgroup of methods and devices because when different positions areselected, different tissues and organs surrounding those that are understudy are irradiated).

Higher resolving power in the second group of means, requiring a greaternumber of irradiations from different positions, is limited, first ofall, due to inadmissible growth of the dosage. Technical means foracquiring primary data and further image reconstruction is quite complexdue to necessity of using fast computers with special software andhigh-precision requirements to the mechanical structural elements, whichmust guarantee correct localization of one and the same resolutionelements in the target area during their irradiation from differentpositions. The latter is caused by the fact that the imagereconstruction calculations must use the actual data obtained fromdifferent irradiation cycles but referring to one and the sameresolution elements.

The second above mentioned group of methods and devices, where discretedata on the density of each of the resolution elements is obtained, isthe closest one to what is suggested.

SUMMARY OF THE INVENTION

The technical result, which the suggested inventions are aimed at,consists in higher accuracy of determining relative indices of theobject's substance density in the acquired image together with avoideduse of complex and expensive technical means. When the suggestedinventions are used for diagnostic purposes in medicine and otherinvestigations related to the action on biological objects, the achievedresult consists also in reduced dosage of radiation of tissuessurrounding the tissues under study.

To obtain the said types of technical results, in the suggested X-raymethod of producing the image of the internal structure of an object,the X-rays are concentrated in a zone, which is located inside the areaunder study (which area is hereinafter referred to as the target area)of the object. Secondary radiation (scattered Compton coherent andnon-coherent, fluorescent radiation), excited in this zone, istransported to one or more detectors. Scanning of the target area of theobject is done by way of moving the zone of concentration. The resultsof measurement at each current position of the zone of concentration(X-rays concentration zone) are attributed to one of the points insidethis zone. Movement of the zone of concentration during scanning isfollowed by simultaneous determination and fixation of coordinates ofthis zone. Judgment on the density of the object's substance in thispoint is made based on the population of intensity values of thesecondary radiation, which are obtained with the help of one or moredetectors and which are determined simultaneously with the coordinatesof the said current point. The obtained values, recognized as thedensity indices of the object's substance, together with respectivevalues of coordinates, are used for building up a picture of thesubstance density distribution in the object's target area. Movement ofthe X-ray concentration zone for scanning the object's target area isdone by way of relative movement of the object under study and the X-raysources, which relative position between themselves remains stable,together with the X-ray concentration means, means for secondaryradiation transportation to the detectors, and the detectors themselves.

It is to be understood that the X-rays concentration is done with thehelp of several, i.e., more than one, concentration means, using severalof spaced apart x-ray sources, the beans of which reach the x-rayconcentration zone via different routes, so those beams are notsummarized in the object's parts outside of the x-ray concentrationzone.

A common feature for the known from ([2], pp. 138–146, [3], pp. 471–472)and suggested methods is the action on the object under study withX-rays during relative movement of the object under study and the X-rayoptical system including X-ray sources together with their control unitsand detectors.

One of the differences of the suggested method consists in the presenceof the operation of concentrating X-rays in the zone covering thecurrent point, in which it is required to determine a density value (acurrent point, to which the measurement results are attributed).Scanning, which presence is a common feature of the known and suggestedmethods, is done in a totally different way in case of the latter—byshifting the current position of the X-rays concentration zone into thevicinity of the next point, for which it is desirable to determine thedensity of the substance of the object under study. The differenceconsists also in the operation of transportation of the secondaryradiation (scattered Compton coherent and non-coherent radiation,fluorescent radiation), excited in this zone, from the concentrationzone to the detector (detectors).

In this instance, it is not the radiation of the source itself, whichpassed through the object under study, that renders action on thedetector (detectors), but the said secondary radiation. Intensity of thelatter, as is well known (see J. Jackson. Classical Electrodynamics. M.,“Mir”, 1965, pp. 537–538 [4]), when all other conditions are the same,is proportional to the density of the substance, in which this radiationis excited, regardless of the nature of this substance. Thanks to this,secondary scattered radiation, which is a nuisance factor in the knownmethod, becomes an informative factor. Usage of current values of thesecondary radiation intensity as an index of the substance density isanother difference of the suggested method.

Differences of the suggested method from the known one are alsocharacterized below, in the description of possible particular cases ofits embodiment, providing for using various combinations of X-raysconcentration means and transportation means for the secondary scatteredradiation.

In one of such particular cases, X-rays concentration in the zonecovering the current point, to which the measurement results areattributed, is done using one or more collimators. In this case, arespective number of space-apart X-ray sources are used. Transportationof the excited secondary radiation to one or more detectors is also doneusing one or more collimators, where all collimators are oriented sothat the axes of their central channels would cross in the currentpoint, to which the measurement results are attributed.

In another particular case, X-rays concentration in the zone is doneusing one or more X-ray hemilenses transforming divergent radiation of arespective number of X-ray sources into quasi-parallel radiation.Transportation of the excited secondary radiation to one or moredetectors is done, in this case, using one or more X-ray hemilenses orlenses, focusing this radiation on the detectors. It is also possible toperform transportation of the secondary radiation to one or moredetectors using one or more hermilenses forming quasi-parallelradiation. In this case, all X-ray lenses and hemilenses are oriented sothat their optical axes would cross in the current point, to which themeasurement results are attributed.

In still another particular case X-rays concentration in the zone isdone using one or more X-ray hemilenses transforming the divergentradiation of a respective number of space-apart sources intoquasi-parallel radiation, while transportation of the excited secondaryradiation to one or more detectors is done using one or morecollimators. In this case, the X-ray hemilenses and collimators areoriented so that the optical axes of all X-ray hemilenses and centralchannels of all collimators would cross in the current point, to whichthe measurement results are attributed.

X-rays concentration can be also done using one or more space-apartX-ray sources and a respective number of X-ray lenses focusing thedivergent X-rays from each of the sources directly in the current point,to which the measurement results are attributed; while transportation ofthe excited secondary radiation to one or more detectors is done usingX-ray lenses focusing this radiation on the detectors and having asecond focus in the said point.

Another particular case differs from the previous one in that thetransportation of excited secondary radiation to one or more detectorsis done using collimators oriented so, that the optical axes of theircentral channels would cross in the output focus of the lens focusingdivergent radiation from the source (in the common focus of more thanone such lenses if more than one sources are used).

The suggested device for producing the image of the internal structureof an object with X-rays comprises a means for positioning the objectunder study, an X-ray optical system, a means for relative movement ofthe means for positioning the object under study and the X-ray opticalsystem, a means for data processing and imaging. The device alsocomprises sensors for determining the coordinates of the current point,to which the measurement results are attributed and which is locatedinside the target area. These sensors are linked to the means forpositioning of the object under study and the X-ray optical system andconnected through their outlets to the means for data processing andimaging. The X-ray optical system comprises one or more X-ray sources,means for concentration of the radiation from the said one or more X-raysources in the zone covering the current point, to which the measurementresults are attributed. In addition the X-ray optical system comprisesone or more means for transportation of the excited secondary radiationand placed at their exits detectors of this radiation. The outlets ofthe said detectors are connected to the means for data processing andimaging.

A common feature of the known and suggested devices is the presence ofthe means for positioning the object under study, an X-ray opticalsystem, a means for relative movement of the means for positioning theobject under study and the X-ray optical system, coordinate sensors, andthe means for data processing and imaging.

In contrast to the known device, the X-ray optical system in thesuggested device comprises means for concentration of the radiation fromone or more sources in the zone covering the current point, to which themeasurement results are attributed. In addition, the X-ray opticalsystem comprises one or more means for transportation of the excitedsecondary radiation to the detectors of this radiation. Thanks to this,it is this radiation that is input to the detectors but not theradiation from the source (sources) after it has passed through theobject under study. The coordinate sensors in the suggested devicefulfill another function compared with the known device—they are usedfor determining coordinates of the current point, to which themeasurement results are attributed. The function of the means for dataprocessing and imaging is also different—this means acts based on theinput carrying direct data on the substance density and coordinates ofthe current point, to which these data are attributed. The design of thesuggested device and its principle of operation create prerequisites fora situation, when there is no dependence on the accuracy or resolvingpower, since the performance characteristics for this device arepractically fully determined by the parameters of the X-raysconcentration means used.

Other differences featured by the suggested device, in various possibleparticular cases of its embodiment, are characterized below.

In one of such particular cases, the X-ray optical system of thesuggested device includes more than one X-ray sources. In this instance,each of the means for X-rays concentration and each of the means fortransportation of the excited secondary radiation to detectors are madeas a collimator with its channels oriented towards the zone ofconcentration of the radiation from the X-ray sources. The optical axesof the central channels of all collimators cross in the current point,to which the measurement results are attributed.

In this particular case, the X-ray sources incorporated in the X-rayoptical system can be quasi-point. The collimators have channels thatare all focused on these sources and are fanning (widening) towards themeans for positioning the object under study. Between the exit from eachX-ray source and entrance to a respective collimator, there is a screenwith an opening.

In the same particular case, the X-ray sources incorporated in the X-rayoptical system can be extended X-ray sources. In this instance, thecollimators have channels that are all coming together (narrowing down)towards the means for positioning the object under study.

In another particular case of embodiment of the suggested device, theX-ray sources incorporated in the X-ray optical system are quasi-pointsources; each of the means for X-rays concentration is made as an X-rayhemilens transforming the divergent radiation of a respective sourceinto quasi-parallel radiation; while each of the means fortransportation of the excited secondary scattered Compton radiation tothe detector is made as an X-ray hemilens focusing this radiation on thedetector. In this instance, the optical axes of all X-ray hemilensescross in the current point, to which the measurement results areattributed.

In the next particular case of embodiment of the suggested device, sameas in the previous one, the X-ray sources incorporated in the X-rayoptical system are quasi-point sources, and each of the means for X-raysconcentration is made as an X-ray hemilens transforming the divergentradiation of a respective source into quasi-parallel radiation. But incontrast to the previous case, each of the means for transportation ofthe excited secondary radiation to the detector is made as an X-rayhemilens with its focus in the current point, to which the measurementresults are attributed, which hemilens transforms the said radiationinto quasi-parallel radiation and directs it to the detector. In thisinstance, the optical axes of all X-ray hemilenses cross in the currentpoint, to which the measurement results are attributed.

In still another particular case, the X-ray sources incorporated in theX-ray optical system are also quasi-point sources; each of the means forX-rays concentration is made as an X-ray hemilens transforming thedivergent radiation of a respective source into quasi-parallelradiation. But in contrast to the previous case, each of the means fortransportation of the excited secondary radiation to the detector ismade as an X-ray lens focusing this radiation on the detector and havinga second focus in the X-rays concentration zone. The optical axes of allX-ray hemilenses and lenses cross in the current point, to which themeasurement results are attributed.

In the next particular case, same as in the previous two, the X-raysources incorporated in the X-ray optical system are quasi-point, andeach of the means for X-rays concentration is made as an X-ray hemilenstransforming the divergent radiation of a respective source intoquasi-parallel radiation. In this instance, each of the means fortransportation of the excited secondary radiation to the detector ismade as a collimator with channels that are all fanning (widening)towards a respective detector. The optical axes of all X-ray hemilensesand central channels of collimators cross in the current point, to whichthe measurement results are attributed.

The X-ray optical system of the suggested device can be made as followstoo. The X-ray sources incorporated therein are quasi-point sources;each of the means for X-rays concentration is made as an X-ray hemilenstransforming the divergent radiation of a respective X-ray source intoquasi-parallel radiation; while each of the means for transportation ofthe excited secondary Compton radiation to the detector is made as acollimator with channels that are all coming together (narrowing down)towards a respective detector. The optical axes of all X-ray hemilensesand central channels of collimators cross in the current point, to whichthe measurement results are attributed.

Another embodiment of the suggested device is also possible, where theX-ray sources incorporated in the X-ray optical system are quasi-pointsources; each of the means for X-rays concentration is made as an X-raylens focusing the divergent radiation of the X-ray source. In thisinstance, each of the means for transportation of excited secondaryradiation to the detector is made as an X-ray lens focusing thisradiation on a respective detector. The optical axes of all X-ray lensescross in the current point, to which the measurement results areattributed.

Next particular case of embodiment of the suggested device ischaracterized by the fact that the X-ray sources incorporated in theX-ray optical system are quasi-point sources; each of the means forX-rays concentration is made as an X-ray lens focusing the divergentradiation of the source; while each of the means for transportation ofthe excited secondary radiation to the source is made as a collimatorwith its channels narrowing down (coming together) towards a respectivedetector. In this instance, the optical axes of all X-ray lenses andcentral channels of collimators cross in the current point, to which themeasurement results are attributed.

One more particular case of the device embodiment is characterized bythe fact that the X-ray sources incorporated in the X-ray optical systemare quasi-point sources; each of the means for X-rays concentration ismade as an X-ray lens focusing the divergent radiation of the X-raysource; while each of the means for transportation of the excitedsecondary Compton radiation to the detector is made as a collimator withchannels widening (fanning) towards a respective detector. In thisinstance, the optical axes of all X-ray lenses and central channels ofcollimators cross in the current point, to which the measurement resultsare attributed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 clarifies the principles, on which the suggested method is based,giving a schematic diagram of positional relationships and connectionsbetween the basic components of the device embodying the suggestedmethod;

FIGS. 2 and 3 show particular cases of method embodiment and the devicemake, where collimators are used for X-rays concentration andtransportation of the secondary radiation to detectors;

FIGS. 4 and 5 show the same with the exception that here X-rayhemilenses are used;

FIG. 6 shows the same with the exception that here X-ray hemilenses areused for X-rays concentration and “full” X-ray lenses are used fortransportation of the secondary radiation to the detectors;

FIGS. 7 and 8 show the same with the exception that here X-rayhemilenses are used for X-rays concentration and collimators are usedfor transportation of the secondary radiation to detectors;

FIG. 9 shows the same with the exception that here X-ray lenses are usedfor X-rays concentration and transportation of the secondary radiationto the detectors;

FIGS. 10 and 11 show the same with the exception that here X-ray lensesare used for X-rays concentration and collimators are used fortransportation of the secondary radiation to the detectors.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS OF THE INVENTION

The preferred method is embodied with the help of the suggested deviceas following.

Divergent X-rays from a quasi-point source (FIG. 1) is focused by theX-ray lens 2 in the specified current point 4 within the target area 7of an object 5 (for example, a biological object). The latter ispositioned as necessary with the help of the means 10 for positioning.Focused in current point 4, radiation excites secondary scatteredradiation in the substance of object 5 (coherent and non-coherentCompton radiation, fluorescent radiation). The intensity of secondaryradiation is proportional, with the accuracy of the fluctuations due tothe stochastic nature of the process of secondary radiation excitation,to the density of the substance where it is excited. The focus of thesecond X-ray lens 3 is located in the same current point 4. This secondlens focuses the scattered radiation that it has captured onto detector6, which converts it into an electric signal that is input to the means12 for data processing and imaging. The position of the common focuspoint of lenses 2 and 3 in point 4 is selected by way of relativemovement of the means 10 for object positioning and a group of thedevice elements referred to as the X-ray optical system 8 comprising theX-ray source 1, the X-ray lenses 2 and 3, and the detector 6 of thesecondary radiation.

It should be explained that lenses used for controlling X-rays (focusingthe divergent radiation, formation of a quasi-parallel beam fromdivergent radiation, focusing quasi-parallel beam and so on) are a onewhole of curved channels transporting the radiation, within which theradiation experiences multiple total external reflection (see, forinstance: Arkadiev V. A., Kolomiytsev A. I., Kumakhov M. A. et al.Broadband X-ray optics with wide angular aperture. The Progress ofPhysics, 1989, vol. 157, issue 3, p. 529–537 [6], where the first lensof this type is described; U.S. Pat. No. 5,744,813 (published Apr. 28,1998) [7], where the modern lens is described). On the whole, the lensis shaped as a barrel (i.e. it narrows down towards both ends), if it isdesigned for focusing the divergent radiation; or as a half-barrel (i.e.it narrows down to one of the two ends only), if it is designed fortransformation of divergent radiation into quasi-parallel radiation, orfor focusing such divergent radiation. The terms “full lens” and“hemilens” are widely used to determinate the lenses of two said types.

There are two options of the device operation according to FIG. 1. Oneoption is to have the means 10 for positioning the object under studystable together with the object 5 under study located therein, while theX-ray optical system 8 is moved (the possibilities of its movement areshown by arrows 9 on FIG. 1), where the positional relationship ofelements 1, 2, 3, and 6 remains fixed (consequently, coincidence offocuses of lenses 2 and 3 is preserved). The other option, on thecontrary, is to have the X-ray optical system 8 fixed, while the means10 for positioning of the object under study together with this objectunder study 5 is moved. Expediency of implementing one or the otheroption depends on the size and weight of object 5 compared to the sizeand weight of the group of above listed elements making the X-rayoptical system 8.

The device also includes a coordinate sensor 11 that reacts to therelative movement of the X-ray optical system 8 and the means 10 forpositioning of the object under study and is connected to the latter.Sensor 11 should be adjusted so as to form signals that would beproportional to the current coordinates of the common focal point oflenses 2 and 3 in point 4 relatively to the selected reference pointlinked to the means 10 for positioning of the object under study. Outputsignals from sensor 11 and the output signal from detector 6 are inputto the means 12 for data processing and imaging. Focal point in point 4,in this case, is the current point, to which the measurement results areattributed and in which vicinity (with regard to the final size of thefocal zone of X-ray lens 2), the radiation from the source 1 is actuallyconcentrated. Means 12 for data processing and imaging provides forreproduction of the picture of density distribution in the object'ssubstance through implementation of this or other two- orthree-dimensional imaging algorithm (see, for instance, E. Lapshin.Graphics for IBM PC. M., “Solon”, 1995 [5]). In the simplest case, when,for example, scanning (movement of the X-rays concentration zone thatincludes current point 4, to which the measurement results areattributed) is done in any flat cross-section of object 5, concurrentlyimage rastering goes on the screen of means 12 with a prolongedafterglow; it is also possible to save a certain amount of measurements'results provided with a later periodic image rastering, etc.

The principle of operation of the suggested inventions is based on thefact that the intensity of secondary scattered Compton radiation (theprobability of appearance of quanta of this radiation), when all otherconditions are the same (in particular, in case of the same intensity ofprimary X-rays acting on the substance), is proportional to thesubstance density.

As has been noted above in the subject matter of the suggested methodand device, the main difference of these inventions consists in usingquanta of the scattered secondary Compton radiation as informative incontrast to known methods and devices where they are an adverse factor.

As has been noted, in medical applications an important advantage of thesuggested inventions is the possibility of obtaining acceptable accuracyat lower dosage received by biological tissues.

To assess possible benefit, let's make the following assumptions: energyof photons E=50 keV, X-rays concentration zone is located at 50 mm depthand has the size of 1 mm×1 mm×1 mm (such values are typical, forexample, for observation conditions and accuracy in mammographyexaminations); the detector registers 5% of the secondary radiation thatwas excited at the depth of 5 cm (this assumption means that secondaryradiation, before it enters the means for its transportation to thedetector, passes 5 cm in the patient's body; in this instance the angleof capture of a lens or a collimator delivering secondary radiation tothe detector makes 0.05×4π steradian). Considering that photons' linearattenuation coefficient in a patient's body is close to that typical forwater at E=50 keV energy and equals approximately to 2×10⁻¹ l/cm, wederive, that when the primary X-ray beam reaches the depth of 5 cm, itsintensity falls down in exp(2×10⁻¹×5)=e≈2.71 times. When the secondaryradiation (which photon energy is also very close to 50 keV), leaves thepatient's body, its intensity also falls down in e≈2.71 times. Hence,the total intensity loss due to radiation absorption in the patient'sbody will make e×e≈7.3 time. Understating the assessed benefit, we willtake into consideration only the Compton component of secondaryradiation. At depth Δx, the probability of secondary Compton radiationformation equals to ω=σ_(k)×N_(e)×Δx, where σ_(k)=6.55×10⁻²⁵ cm² is thecross-section of secondary Compton scattering; N_(e)=3×10²³ l/cm³ is thedensity of electrons in water. Thus, at Δx=1 mm=10⁻¹ cm probability isω=6.55×10⁻²⁵×3×10²³×10⁻¹≈2×10⁻². In other words, formation of onesecondary photon at the length of Δx=1 mm requires on average 1:(2×10⁻²)=50 photons of the primary radiation.

Let's put a precondition that the error of density assessment (i.e. theerror with which the quantity (number) of secondary photons isdetermined) is of the order of 1%. With regard to the probabilisticnature of the process, the root-mean-square value of the relative errorequals to δ=1/(N)^(1/2), where N is the number of registered photons.N=10000 corresponds to δ=0.01.

Now we can set up a simple equation for N_(x), i.e. the required numberof primary photons penetrating to the 5 cm depth and exciting, at thisdepth, secondary Compton radiation, which, in its turn, passes 5 cm toreach the detector; in this instance, N=10000 photons reach thedetector:N _(x) ×e ⁻²×5×10⁻²×2×10⁻²=10⁴.

Here coefficient 5×10⁻² means that out of the total number of generatedsecondary photons, only 5%=10⁻² reach the detector and get registered.We obtain from the equation that N_(x)=7.3×10⁷.

Photons featuring energy E=50 keV produce a dose of radiation equal to 1Roentgen, if their flux equals to 2.8×10¹⁰ l/cm² (for table data showingthe correlation between photon energy, their number and dose see, forexample, [2]). If the cross-section of the primary X-rays at their entryto the patient's body is assumed equal to 1 cm², then the flux of7.3×10⁷ l/cm² will produce in the patient's body a dose of radiationequal to 2.6×10⁻³ Roentgen.

During traditional X-ray tomography, for example, during osteoporosisexamination, the dosage usually makes 100÷300 milliroentgen, (V. I.Mazurov, E. G. Zotkin. Topical questions of osteoporosis diagnostics andtreatment. Saint-Petersburg, IKF “Toliant”, 1998, p. 47 [8]), i.e.approximately 100 times higher.

Dosage can be further decreased several times if exposure is done usingseveral sources, which beams reach the X-rays concentration zone viadifferent routs, so those beams are not summarized in the patient'sbody.

Therefore, such options of embodiment of the suggested method anddevices are more expedient, where several space-apart X-ray sources andX-ray detectors are used together with a respective number of the meansfor X-rays concentration and means for transportation of the secondaryCompton radiation to the detectors (lenses, hemilenses, collimators). Onone hand, it enables a more efficient X-rays concentration (in case of asole the means for X-rays concentration, this is possible only using anX-ray lens as shown on FIG. 1) and better signal-to-noise ratio at thedetector's outlet. On the other hand, this allows achieving a moredistributed action of X-rays on the object under study and avoiding overdosage for the object's parts not subjected to examination. When, underall other equal conditions, several detectors and simple averaging areused (or a more complicated processing of outputs from differentdetectors in means 12 for data processing and imaging, as, for example,a “weighted” averaging or processing taking into account correlation ofdensities in the closely located points), this permits using lesspowerful X-ray sources without compromising the accuracy. Besides,averaging leads to less impact rendered by other factors that decreaseaccuracy (for example, unequal absorption of X-rays from the sources ontheir route to different points in which the density is determined, andthat of secondary radiation on the route from such points to the entriesof the means for transportation of the secondary Compton radiation tothe detectors).

These are such options that are discussed below (FIGS. 2 to 11).

In terms of technical embodiment, the options shown in FIG. 2 and FIG. 3are the simplest.

In the diagram on FIG. 2, quasi-point X-ray sources 1 and collimators 13are used; the channels of collimators are fanning (widening) in thedirection of radiation propagation to concentrate the radiation in zone16. Between the sources 1 and collimators 13, there are screens 14 withopenings for radiation transmission to the collimators' entries and forprevention of its direct action (aside the collimators) on the object.Secondary radiation is transported to detectors 6 with the help ofcollimators 15, which channels are coming together (narrowing down) inthe direction of radiation propagation, i.e. towards detectors 6, andwhich can have a focus on the sensing surface of the latter. Forinstance, semiconductor detectors with small entrance aperture can beused as detectors 6.

In FIG. 3 the collimator's orientation is opposite to that shown in FIG.2. To achieve utmost use of the entrance aperture of collimators 18,which concentrate radiation in zone 16, it is better to use extendedX-ray sources 17. For the same reason, it is better to use detectors 20featuring large entrance aperture (for example, scintillationdetectors).

In FIG. 4, the X-rays concentration means for concentration of theradiation from quasi-point sources 1 and the means for transportation ofthe secondary radiation are made, correspondingly, as X-ray hemilenses21 and 22. In this instance, hemilenses 22 focus secondary radiation ondetectors 6.

In FIG. 5, the X-rays concentration means concentrating radiation fromquasi-point sources 1, and the means for transportation of the secondaryradiation are made as hemilenses 21 and 23, correspondingly. In thisinstance, hemilenses 23 transform scattered secondary radiation intoquasi-parallel radiation and direct this quasi-parallel radiation todetectors 20 featuring large entrance aperture.

FIG. 6 shows a combined option, when the X-rays concentration meansconcentrating radiation from quasi-point sources 1 are made as X-rayhemilenses 21, which direct parallel beams towards zone 16; while themeans for transportation of the secondary Compton radiation to detectors6 are made as “full” X-ray lenses 3.

FIGS. 7 and 8 show other combinations that differ from the previous onein that the means for transportation of the secondary Compton radiationto detectors are made as collimators.

In FIG. 7, collimators 19 have channels widening towards detectors 20,while the latter have a large entrance aperture.

In FIG. 8, on the contrary, collimators 15 have channels narrowing downtowards detectors 6, while the latter have a small entrance aperture.

FIG. 9 shows the most effective option in terms of accuracy andresolution, where the X-rays concentration means concentrating radiationfrom quasi-point sources 1 and the means for transportation of thesecondary radiation to detectors 6 are made as “full” lenses 2 and 3,respectively, (compare this option with the one shown in FIG. 1).

FIGS. 10 and 11 show two more combined options. Their common feature isthat in both cases “full” X-ray lenses 2 are used as the X-raysconcentration means concentrating radiation from quasi-point sources 1.

In FIG. 10 collimators 15 narrowing down towards the detectors are usedas the means for transportation of the secondary radiation to detectors6 featuring small aperture.

In FIG. 11 collimators 19 widening towards the detectors are used as themeans for transportation of the secondary Compton radiation to detectors20 featuring large aperture.

Utilization of one or another scheme of the method embodiment and designof the device depends both on the availability of such effective meansfor radiation concentration and transportation as X-ray lenses andhemilenses, and on the required resolution. The latter affects alsoselection of parameters for lenses and hemilenses (such as the focalspot size, length of the focus zone in the direction of the lens'optical axis, and others). This is done also taking into considerationthat implementation of quite high resolution, when “full” lenses areused (of the order of some sections of a millimeter or higher), iscoupled with longer time required for scanning of the object's targetarea. Other circumstances are also taken into account, such asavailability of X-ray sources of suitable power and dimensions, andothers.

Availability of the described and many other options of the suggestedmethod embodiment and the suggested device outlays provide widepossibilities for designing intra-vision means that would satisfyspecific demands.

REFERENCES

1. The Polytechnic Dictionary. M., “Soviet Encyclopedia”, 1976.

2. The Physics of Image Visualization in Medicine. Ed. by S. Webb. M.,“Mir”, 1991.

3. V. V. Piklov, N. G. Preobrazhenskiy. Computational Tomography andPhysics Experiment. The Progress of Physics, v. 141, Issue 3, November1983.

4. J. Jackson. Classical Electrodynamics. M., “Mir”, 1965

5. E. Lapshin. Graphics for IBM PC. M., “Solon”, 1995

6. V. A. Arkadiev, A. I. Kolomiytsev, M. A. Kumakhov, and others.Broad-band X-ray Optics with Large Angular Aperture. The Progress ofPhysics, 1989, v. 157, Issue 3.

7. The U.S. Pat. No. 5,744,813 (published Apr. 28, 1998).

8. V. I. Mazurov, E. G. Zotkin. The Topical Questions of OsteoporosisDiagnostics and Treatment. Saint-Petersburg, IKF “Foliant”, 1998.

1. A method for producing an image of the internal structure of anobject with X-rays, wherein said object is subjected to X-rays and theoutput from multiple X-ray detectors is used for obtaining data on thesubstance density of said object; the method including the steps of:emitting multiple X-ray beams by multiple X-ray sources spaced apartwith respect to each other, concentrating the X-ray beams in an X-rayconcentration zone located within a target area of said object, theX-ray beams being concentrated using multiple concentration elementscausing said X-ray beams to reach said X-ray concentration zone viamultiple paths so as to sum effect of said X-rays beams in said X-rayconcentration zone and avoid summing the effect of said X-ray beams inportions of said object outside of said X-ray concentration zone;transporting secondary radiation excited in said X-ray concentrationzone to the multiple detectors via multiple paths using multiplecorresponding transportation elements; determining the substance densityof the object in a current point of the target area based on multipleintensity values of the secondary radiation obtained for the currentpoint using the multiple detectors, the intensity values beingdetermined concurrently with determining coordinates of the currentpoint; scanning the target area by moving said X-ray concentration zoneto a next point in the target area, the scanning being performed byproviding relative movement of the X-ray sources, the concentrationelements, the transportation elements and the detectors with respect tothe object; and producing a density distribution picture for said targetarea based on determined intensity values for points being scanned inthe target area and determined coordinates of the respective points. 2.The method of claim 1, wherein the step of concentrating the X-ray beamsincludes using as the concentration elements, a plurality of collimatorsequal in number to said multiple spaced apart X-ray sources; saidtransporting of said secondary radiation from said X-ray concentrationzone to said multiple detectors being performed using as thetransportation elements, corresponding number of collimators havingcentral channels, and orienting said collimators so that the axes ofsaid central channels cross in said current point.
 3. The method ofclaim 1, wherein the step of concentrating said X-rays includes using asthe concentration elements, multiple first X-ray hemilenses fortransforming divergent radiation from a respective number of said spacedapart X-ray sources into quasi-parallel radiation; said transporting ofsaid secondary radiation excited in said X-ray concentration zone beingperformed using as the transportation elements, multiple second X-rayhemilenses for focusing said secondary radiation on said detectors orforming quasi-parallel radiation incident onto said detectors, andorienting said second X-ray hemilenses so that their optical axes crossin said current point.
 4. The method according to claim 1, wherein thestep of concentrating the X ray beams is performed using as theconcentration elements, multiple X-ray hemilenses for transformingdivergent radiation from a respective number of spaced apart X-raysources in quasi-parallel radiation, transporting secondary radiation,which is excited in the X-ray concentration zone, to the multipledetectors using as the transportation elements, corresponding number ofX-ray lenses for focusing this radiation on the detectors; and orientingall of said X-ray hemilenses and lenses so that their optical axes crossin the current point.
 5. The method according to claim 1, wherein thestep of concentrating the X-ray beams using as the concentrationelements, multiple X-ray hemilenses for transforming divergent radiationfrom a respective number of spaced apart X-ray sources intoquasi-parallel radiation; transporting secondary radiation, which isexcited in the X-ray concentration zone, to the multiple detectors usingas the transportation elements, multiple collimators; orienting saidX-ray hemilenses and said collimators so that the optical axes of allX-ray hemilenses and central channels of all collimators cross in thecurrent point.
 6. The method according to claim 1, wherein the step ofconcentrating the X-ray beams is performed using as the concentrationelements, multiple X-ray lenses for focusing divergent X-rays from arespective number of spaced apart X-ray sources; transporting secondaryradiation, which is excited in the X-ray concentration zone, to saidmultiple detectors using as the transportation elements, correspondingnumber of X-ray lenses focusing this radiation on said detectors.
 7. Themethod according to claim 1, wherein the step of concentrating the X-raybeams is performed using as the concentration elements, multiple X-raylenses for focusing divergent X-rays from respective number of spacedapart X-ray sources; and transporting secondary radiation, which isexcited in the X-ray concentration zone, to said multiple detectorsusing as the transportation elements corresponding number ofcollimators.
 8. Apparatus for producing an image of the internalstructure of an object said apparatus including: a holding device forholding said object; an X-ray optical system for providing X-rayradiation and determining radiation intensity; a moving device forproviding relative movement between the holding device and the X-rayoptical system to scan a target area of the object, a coordinate sensingdevice for determining coordinates of points in the target areacorresponding to relative positions between the holding device and theX-ray optical system, and a processing device coupled to the X-rayoptical system and the coordinate sensing device for processinginformation to produce the image; the X-ray optical system including:multiple X-ray sources spaced apart with respect to each other forproducing multiple X-ray beams, multiple X-ray concentration elementsfor concentrating the multiple X-ray beams in an X-ray concentrationzone located within the target area of the object, the X-rayconcentration elements causing the X-ray beams to reach the X-rayconcentration zone via multiple paths so as to sum effect of the X-raysbeams in the X-ray concentration zone and avoid summing the effect ofthe X-ray beams in portions of the object outside of the X-rayconcentration zone, multiple transportation elements for transportingsecondary radiation excited in the X-ray concentration zone via multiplepaths, and multiple X-ray detectors corresponding to the multipletransportation elements and arranged for determining intensity of thesecondary radiation for a current point in the target area; the currentpoint corresponding to a current relative position between the holdingdevice and the X-ray optical system, the coordinate sensing system beingconfigured for determining coordinates of the current point, and theprocessing device being configured for receiving values of the intensitydetermined by the multiple X-ray detectors and for producing the imageof the internal structure of the object based on the values of theintensity for various points being scanned in the target area and thecoordinates of the respective points.
 9. Apparatus according to claim 8,wherein said X-ray sources are quasi-point X-ray sources; each of saidX-rays concentration elements being comprised of an X-ray hemilens fortransforming divergent radiation from a respective X-ray source intoquasi-parallel radiation; and each of said multiple X-ray transportationelements for transportation of secondary radiation to said X-raydetectors is comprised of an X-ray hemilens for focusing said secondaryradiation onto a respective X-ray detector; and wherein the optical axesof all X-ray hemilenses cross in said current point.
 10. Apparatusaccording to claim 8, wherein said X-ray sources are quasi-point X-raysources; each of said X-rays concentration elements being comprised ofan X-ray hemilens transforming divergent radiation from a respectiveX-ray source into quasi-parallel radiation; and each of saidtransportation elements for transportation of secondary radiation tosaid X-ray detectors is comprised of an X-ray hemilens for formingquasi-parallel radiation and having a focus in said X-rays concentrationzone; wherein the optical axes of all X-ray hemilenses cross in saidcurrent point.
 11. Apparatus according to claim 8, wherein said X-raysources are quasi-point X-ray sources; each of said X-rays concentrationelements being comprised of an X-ray hemilens for transforming divergentradiation from a respective X-ray source into quasi-parallel radiation;and each of said transportation elements for transportation of secondaryradiation to said X-ray detector is comprised of an X-ray lens includinga first focus for focusing said secondary radiation onto a respectiveX-ray detector and having a second focus in said X-rays concentrationzone; wherein optical axes of all X-ray hemilenses and X-ray lensescross in said current point.
 12. Apparatus according to claim 8, whereinsaid X-ray sources are quasi-point X-ray sources; each of said X-raysconcentration means being comprised of an X-ray hemilens fortransforming divergent radiation from a respective X-ray source intoquasi-parallel radiation; each of said transportation elements fortransportation of secondary radiation to respective X-ray detector beingcomprised of a collimator including channels fanning towards therespective X-ray detector; and wherein optical axes of each saidhemilens and central channels of each said collimator cross in saidcurrent point.
 13. Apparatus according to claim 8, wherein said X-raysources are quasi-point X-ray sources; each of said X-rays concentrationelements being comprised of an X-ray hemilens for transforming divergentradiation from a respective X-ray source into quasi-parallel radiation;each of said transportation elements for transportation of secondaryradiation to a respective X-ray detectors being comprised of acollimator, including channels coming together towards the respectiveX-ray detector; and wherein the optical axes of all X-ray hemilenses andcentral channels of each said collimator cross in said current point.14. Apparatus according to claim 8, wherein said X-ray sources arequasi-point X-ray sources; each of said X-rays concentration elementsbeing comprised of an X-ray lens for focusing divergent radiation from arespective X-ray source; each of said transportation elements fortransportation of secondary radiation to an X-ray detector beingcomprised of an X-ray lens for focusing said secondary radiation onto arespective detector; and wherein optical axes of all X-ray lenses crossin said current point.
 15. Apparatus according to claim 8, wherein saidX-ray sources are quasi-point X-ray sources; each of said X-raysconcentration elements being comprised of an X-ray lens for focusingdivergent radiation from a respective X-ray source; each of saidtransportation elements for transportation of secondary radiation tosaid X-ray detector being comprised of a collimator including channelscoming together towards a respective detector; and wherein optical axesof all X-ray lenses and central channels of each said collimator crossin said current point.
 16. Apparatus according to claim 8, wherein saidX-ray sources are quasi-point X-ray sources; each of said X-raysconcentration elements being comprised of an X-ray lens for focusingdivergent radiation from a respective X-ray source; each of saidtransportation elements for transportation of secondary radiation to adetector being comprised of a collimator including channels fanningtowards a respective detector; wherein optical axes of all X-ray lensesand central channels of each collimator cross in said current point.